Vapochromic luminescent proton conductors: switchable vapochromism and proton conduction of luminescent Pt(ii) complexes with proton-exchangeable sites

Two luminescent and highly proton-conductive Pt(ii) complexes [PtCl(tpypy)]Cl and [PtCl(tpypyH)]Cl-2 (1 and 1 center dot HCl, respectively; tpypy = 2,2 ': 6 ',2 ''-terpyridine-4 ',4 '''-pyridine) were successfully synthesized. X-ray analysis revealed that the intermolecular PtMIDLINE HORIZONTAL ELLIPSISPt interaction was ineffective in the monohydrated form of 1 center dot H2O but effective in dihydrate and hexahydrate forms, 1 center dot HCl center dot nH(2)O (n = 2 and 6). Yellow luminescence (lambda(em) = 519 nm and phi = 0.016) assigned to intraligand (3)pi-pi* phosphorescence was observed for 1 center dot H2O, whereas a stronger red emission ascribable to the phosphorescence from the triplet metal-metal-to-ligand charge transfer ((MMLCT)-M-3) state was observed for the HCl adduct 1 center dot HCl center dot nH(2)O (lambda(em) = 741 nm, phi = 0.06 for n = 2, lambda(em) = 642 nm, and phi = 0.10 for n = 6). Both complexes exhibited strong relative humidity (RH)-dependent proton conductivity, while surprisingly high conductivity was observed for 1 center dot HCl (6.8 x 10(-3) S cm(-1)) at 95% RH at 298 K. The reversible transformation between 1 and 1 center dot HCl was achieved upon exposure to humid HCl gas and heating and their vapochromic behaviour was completely different owing to the presence of acidic N-H protons and the additional hydrophilic Cl- counter anions in 1 center dot HCl. To the best of our knowledge, these complexes are the first switchable vapochromic and highly proton conductive materials that can be employed to visualize the proton conducting state by colour and luminescence.